Heretofore, a method for manufacturing a three-dimensional shaped object by irradiating a powder with a light beam has been known (such method can be generally referred to as “selective laser sintering method”). Such method can produce a three-dimensional shaped object with a plurality of solidified layers stacked integrally by repeating the step (i) of forming a solidified layer by irradiating a predetermined portion of a powder layer with a light beam, thereby allowing sintering of the predetermined portion of the powder or melting and subsequent solidification thereof, and the step (ii) of forming another solidified layer by newly forming a powder layer on the resulting solidified layer, followed by similarly irradiating the powder layer with the light beam (see JP-T-01-502890 or JP-A-2000-73108). The three-dimensional shaped object thus obtained can be used as a metal mold in a case where inorganic powder materials such as a metal powder and a ceramic powder are used as the powder material. While on the other hand, the three-dimensional shaped object can be used as a model or replica in a case where organic powder materials such as a resin powder and a plastic powder are used as the powder material. This kind of technology makes it possible to produce the three-dimensional shaped object with a complicated contour shape in a short period of time.
According to the selective laser sintering method, a three-dimensional shaped object is often manufactured in a chamber which is kept under an inert atmosphere from the viewpoint of the prevention of oxidation or the like. By way of the case of using a metal powder as a powder material and using the resulting three-dimensional shaped object as metal mold, as shown in FIG. 1, a powder layer 22 with a predetermined thickness t1 is firstly formed on a base plate for shaped object 21 (see FIG. 1(a)) and then a predetermined portion of a powder layer 22 is irradiated with a light beam to form a solidified layer 24 on base plate for shaped object 21. Then, a powder layer 22 is newly provided on the solidified layer 24 thus formed and is irradiated again with the light beam to form another solidified layer. In this way, when the solidified layer is repeatedly formed, it is possible to obtain a three-dimensional shaped object with a plurality of solidified layers 24 stacked integrally (see FIG. 1(b)). The solidified layer corresponding to a bottom layer can be formed in a state of being adhered to the surface of the base plate. Therefore, the three-dimensional shaped object and the base plate are mutually integrated. The integrated “three-dimensional shaped object” and “base plate” can be used as a metal mold as they are.
The three-dimensional shaped object obtained by the laser-beam irradiation has a relatively roughened surface. In general, the shaped object has the roughened surface Rz of several hundred micrometers. This is attributed to the fact that the surface of the solidified layer has the adhered powder. When the solidified layer is formed, the energy of the laser beam is changed into heat, which causes the irradiated powder to melt. The melted powder particles are fused with each other during the subsequent cooling step thereof. In this regard, the temperature can be raised in the surrounding powder region of the irradiated point, and thus such surrounding powder tends to adhere to the surface of the solidified layer. This adherence of the powder causes a roughened surface of the three-dimensional shaped object, and thereby a finish processing of surface is necessary therefor. Specifically, the whole surface of the obtained three-dimensional shaped object is required to be subjected to a machining process. For example, as for the obtained three-dimensional shaped object disclosed in JP-T-08-504139, an outer shell portion of the object is subjected to the machining process (see FIG. 16).
According to the actual state of such machining process, consideration is not made on a final use application of the three-dimensional shaped object, and the machining process of the whole exposed surface of the shaped object is performed. For example as for the invention of JP-T-08-504139, the machining process is performed for the whole of the outer shell portion which surrounds the body of the three-dimensional shaped object. This is by no means satisfactory from the viewpoint of the manufacturing cost and time. Moreover, considering that a machining process is generally performed to chip off the surface region for the purpose of obtaining desired form and surface roughness, and it is nothing short of a mechanical process (i.e., process using a machine tool), there is a concern that it causes a damage in the three-dimensional shaped object due to a machining stress (cutting stress) and a machining heat (cutting heat).